It does this by calling the init function of the mimetypes
module. This will have the side effect of modifying the global MIME types
cache in that module.

Multiple file locations containing mime-types can be passed as a list.
The files will be sourced in that order, overriding mime-types from the
files sourced beforehand, but only if a new entry explicitly overrides the
current entry.

Parameters

mimetype_locations

Optional. List of paths to mime.types style files that should
be used. (type: iterable of paths or None)

init

The init function to call. Defaults to the global init
function of the mimetypes module. For internal use (testing)
only. (type: callable)